Analog switch circuits with over-voltage protection are used in various applications, including automotive and industrial applications. Some such analog switch circuits monitor an input voltage and control an external N-channel metal-oxide-semiconductor field-effect transistor (NMOSFET) switching transistor device, which can also be referred to as an NMOS switching transistor device, to isolate a load at the output during an over-voltage condition at the input. For example, some analog switch circuits with over-voltage protection create an onboard reference voltage and then compare that reference voltage to an input voltage to determine whether or not to open the switch. While this works well for a limited range of voltages, it is not believed that such analog switch circuits can protect downstream devices from input voltages significantly higher than the positive power supply voltage rail (Vdd) or lower than the negative power supply voltage rail (Vss).
Most prior analog switch circuits with over-voltage protection use a band-gap reference circuit to produce the aforementioned onboard reference voltage, and a comparator to compare an input voltage signal to that reference voltage. However, the band-gap reference voltage generator and the comparator in those analog switch circuits draw a lot of current, so these over-voltage protected analog switch circuits are not efficient from a power standpoint. More specifically, the above described analog switch circuits typically require a quiescent supply current (Idd) on the order of 10s of microAmps.
Further, the aforementioned analog switch circuits are not believed to provide upstream protection if the over-voltage condition occurs at the output, as opposed to the input. Additionally, the aforementioned analog switch circuits are not believed to provide over-voltage protection when the device within which the switch is located is powered-off. For example, such analog switch circuits may not protect components from a high voltage electrostatic discharge (ESD) event that occurs when the device within which the switch is located is powered-off.